Obama tells ABC's Good Morning America he will act swiftly on the economy
Barack Obama has signed his first executive orders ahead of talks with his military and economic advisers on a packed first full day as US president.
Mr Obama arrived in the Oval Office at 0835 and read a letter left by former President George W Bush. He then went on to Washington's National Cathedral.
Later he announced new ethics rules and a pay freeze for White House staff.
Mr Obama and advisers are to discuss an $825bn rescue economic package - as well as the Iraq and Afghanistan wars.
The president's first day in office has also been dominated by the controversial military trials of terror suspects at Guantanamo. Judges have already agreed to suspend several of the cases requested by Mr Obama.
We will see what Mr Obama does with the history which is now his to shape
As the euphoria surrounding the inauguration dies down, the serious issues of the financial crisis and the wars in Afghanistan and Iraq will top his agenda, correspondents say.
Mr Obama has already ordered last-minute regulations signed by Mr Bush to be put on hold.
Congressional leaders say they intend to pass the economy stimulus bill by the middle of February.
And Mr Obama promised that on his first day in office he would give his military commanders a new mission - to end the war in Iraq.
More than 140,000 US troops are still stationed in Iraq, five years after an invasion which the new president consistently opposed.
President Obama has promised to withdraw combat troops from Iraq within 16 months - and the Iraqi government has said that US forces are welcome to leave before the 2012 deadline set at the end of last year.
Within hours of his inauguration on Tuesday, the new president requested a halt to military trials at the Guantanamo detention camp. Judges have agreed to suspend six cases.
Mr Obama's time for contemplation will be short, correspondents say
They include proceedings against five men accused of plotting the 11 September attacks.
The military judge halted their trial despite the fact that four of the five - including alleged 9/11 mastermind Khalid Sheikh Mohammed - opposed the proposed suspension during a court hearing on Wednesday.
Earlier, the judge in the separate trial of Omar Khadr - a Canadian man accused of killing an American soldier in Afghanistan in 2002 - also agreed to suspend the case.
On Tuesday, Mr Obama and his Secretary of Defence Robert Gates asked for the Guantanamo trials to be suspended for 120 days "in the interests of justice".
Also on Wednesday there will be a debate over the appointment of Hillary Clinton as secretary of state.
Approval for her appointment was postponed after a Republican senator demanded a debate about foreign donations to a foundation headed by her husband, former President Bill Clinton.
Mrs Clinton's nomination is expected to be confirmed in a vote immediately after the debate.
Several other cabinet positions are still to be confirmed.
The US Senate, which traditionally moves swiftly to affirm a new president's cabinet, approved six members on Tuesday, including Janet Napolitano as homeland security secretary and Steven Chu as energy secretary.
Timothy Geithner, the nominee to head the treasury department, faced the Senate finance committee on Wednesday to explain his initial failure to pay payroll taxes he owed while working for the International Monetary Fund.
He apologised to the committee, saying he had been careless but that he had "paid what I owed".
Mr Obama last week called Mr Geithner's tax problems an embarrassment but an "innocent mistake".
Other Obama nominees still to be confirmed are Eric Holder as attorney general, and Tom Daschle as head of health and human services.
The new administration acted quickly after his inauguration to halt measures rushed through in the last days of the Bush administration - a common tactic by new leaders.
Chief of Staff Rahm Emanuel ordered all agencies and departments to stop all pending regulations until a legal and policy review could be conducted, the White House said.
Such a review can be used by an incoming administration to delay so-called "midnight regulations" introduced between November's election and January's inauguration.
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